This project is designed to test whether the cyclic mucleotides maay mediate actions of prolactin or other hormones on uridine uptake and incorporation into RNA in mammary glands of midpregnant mice. Similar studies are being carried out to determine if the cyclic nucleotides affect the rate of casein synthesis in mammary glands. The possibility that hormones affect the activity of enzymes which catalyze the synthesis and degradation of the cyclic nucleotides is also being tested.